A traveller praying in full (itmam)

Question

If a traveller, through forgetfulness, prays four rak‘as and then remembers afterwards, will this prayer be valid, or must he repeat it?

Answer

If, while in the state of legal travel, he performed itmam through forgetfulness and also made the first sitting (qa‘da), the fard has been fulfilled, but because of delaying a wajib, sajda al-sahw is wajib; if he did not perform sajda al-sahw, he should repeat the prayer.

Source: Fatawa Mahmudiyya

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